Pyrogallol protects against influenza A virus‐triggered lethal lung injury by activating the Nrf2–PPAR‐γ–HO‐1 signaling axis

Pyrogallol, a natural polyphenol compound (1,2,3‐trihydroxybenzene), has shown efficacy in the therapeutic treatment of disorders associated with inflammation. Nevertheless, the mechanisms underlying the protective properties of pyrogallol against influenza A virus infection are not yet established. We established in this study that pyrogallol effectively alleviated H1N1 influenza A virus‐induced lung injury and reduced mortality. Treatment with pyrogallol was found to promote the expression and nuclear translocation of nuclear factor erythroid‐2‐related factor 2 (Nrf2) and peroxisome proliferator‐activated receptor gamma (PPAR‐γ). Notably, the activation of Nrf2 by pyrogallol was involved in elevating the expression of PPAR‐γ, both of which act synergistically to enhance heme oxygenase‐1 (HO‐1) synthesis. Blocking HO‐1 by zinc protoporphyrin (ZnPP) reduced the suppressive impact of pyrogallol on H1N1 virus‐mediated aberrant retinoic acid‐inducible gene‐I‐nuclear factor kappa B (RIG‐I–NF‐κB) signaling, which thus abolished the dampening effects of pyrogallol on excessive proinflammatory mediators and cell death (including apoptosis, necrosis, and ferroptosis). Furthermore, the HO‐1‐independent inactivation of janus kinase 1/signal transducers and activators of transcription (JAK1/STATs) and the HO‐1‐dependent RIG‐I‐augmented STAT1/2 activation were both abrogated by pyrogallol, resulting in suppression of the enhanced transcriptional activity of interferon‐stimulated gene factor 3 (ISGF3) complexes, thus prominently inhibiting the amplification of the H1N1 virus‐induced proinflammatory reaction and apoptosis in interferon‐beta (IFN‐β)‐sensitized cells. The study provides evidence that pyrogallol alleviates excessive proinflammatory responses and abnormal cell death via HO‐1 induction, suggesting it could be a potential agent for treating influenza.